Scheduling in License Assisted Access

ABSTRACT

In one aspect, a wireless device receives a scheduling grant and a grant confirmation signal indicating that a network node has performed a CCA on a carrier and is releasing the carrier for the wireless device. An uplink message is transmitted on the carrier without performing a CCA on the carrier. In another aspect, a wireless device is connected to a first cell and a second cell configured on a carrier requiring an LBT protocol. The wireless device receives configuration messages indicating that downlink transmissions on the second cell are to be scheduled. This can mean self-scheduling for downlink on the second cell and cross-carrier scheduling for uplink on the first cell. The wireless device receives a scheduling grant in the first cell and performs a CCA in the second cell. The wireless device then transmits an uplink message responsive to success of the CCA.

TECHNICAL FIELD

This disclosure pertains to scheduling in wireless communicationnetworks, and more particularly to scheduling in wireless networks inwhich data transmissions in unlicensed spectrum are aggregated with datatransmissions in licensed spectrum.

BACKGROUND

The 3GPP initiative “Licensed Assisted Access” (LAA) intends to allowLong Term Evolution (LTE) equipment to also operate in the unlicensed 5GHz radio spectrum. The unlicensed 5 GHz spectrum is used as acomplement to the licensed spectrum. Accordingly, devices connect in thelicensed spectrum (primary cell or PCell) and use carrier aggregation tobenefit from additional transmission capacity in the unlicensed spectrum(secondary cell or SCell). To reduce the changes required foraggregating licensed and unlicensed spectrum, the LTE frame timing inthe primary cell is simultaneously used in the secondary cell.

Regulatory requirements, however, may not permit transmissions in theunlicensed spectrum without prior channel sensing. Since the unlicensedspectrum may have to be shared with other radios of similar ordissimilar wireless technologies, a so called listen-before-talk (LBT)method needs to be applied. Today, the unlicensed 5 GHz spectrum ismainly used by equipment implementing the IEEE 802.11 Wireless LocalArea Network (WLAN) standard. This standard is known under its marketingbrand “Wi-Fi.”

In Europe, the LBT procedure is under the scope of EN 301.893regulation. For LAA to operate in the 5 GHz spectrum, the LAA LBTprocedure shall conform to requirements and minimum behaviors set forthin EN 301.893. However, additional system designs and steps are neededto ensure coexistence of Wi-Fi and LAA with EN 301.893 LBT procedures.

U.S. Pat. No. 8,774,209 B2, titled “Apparatus and method for spectrumsharing using listen-before-talk with quiet periods,” discloses amechanism where LBT is adopted by frame-based orthogonalfrequency-division multiplexing (OFDM) systems to determine whether thechannel is free prior to transmission. A maximum transmission durationtimer is used to limit the duration of a transmission burst, and it isfollowed by a quiet period. However, it is recognized herein that afairer coexistence with other radio access technologies such as Wi-Fi isneeded, while also satisfying EN 301.893 regulations.

LTE uses OFDM in the downlink and discrete Fourier transform(DFT)-spread OFDM, also referred to as single-carrier frequency-divisionmultiple access (FDMA), in the uplink. The basic LTE downlink physicalresource can thus be seen as a time-frequency grid, as illustrated inFIG. 1, where each resource element corresponds to one OFDM subcarrierduring one OFDM symbol interval. The uplink subframe has the samesubcarrier spacing as the downlink and the same number of SC-FDMAsymbols in the time domain as OFDM symbols in the downlink.

In the time domain, LTE downlink transmissions are organized into radioframes of 10 ms, each radio frame consisting of ten equally-sizedsubframes of length Tsubframe=1 ms as shown in FIG. 2. For normal cyclicprefix, one subframe consists of 14 OFDM symbols. The duration of eachsymbol is approximately 71.4 μs.

Furthermore, the resource allocation in LTE is typically described interms of resource blocks, where a resource block corresponds to one slot(0.5 ms) in the time domain and 12 contiguous subcarriers in thefrequency domain. A pair of two adjacent resource blocks in timedirection (1.0 ms) is known as a resource block pair. Resource blocksare numbered in the frequency domain, starting with 0 from one end ofthe system bandwidth.

Downlink transmissions are dynamically scheduled, i.e., in each subframethe base station transmits control information about which terminalsdata is transmitted to and upon which resource blocks the data istransmitted, in the current downlink subframe. This control signaling istypically transmitted in the first 1, 2, 3 or 4 OFDM symbols in eachsubframe and the number n=1, 2, 3 or 4 is known as the Control FormatIndicator (CFI). The downlink subframe also contains common referencesymbols, which are known to the receiver and used for coherentdemodulation of, for example, the control information. A downlinksubframe with CFI=3 OFDM symbols as control is illustrated in FIG. 3.

From LTE Rel-11 onwards, the above described resource assignments canalso be scheduled on the enhanced Physical Downlink Control Channel(EPDCCH). For Rel-8 to Rel-10, only Physical Downlink Control Channel(PDCCH) is available.

The reference symbols shown in FIG. 3 are the cell specific referencesymbols (CRS) and are used to support multiple functions including finetime and frequency synchronization and channel estimation for certaintransmission modes. The PDCCH/EPDCCH is used to carry downlink controlinformation (DCI) such as scheduling decisions and power-controlcommands More specifically, the DCI includes downlink schedulingassignments, including PDSCH resource indication, transport format,hybrid-ARQ information and control information related to spatialmultiplexing (if applicable). A downlink scheduling assignment alsoincludes a command for power control of the physical uplink controlchannel (PUCCH) used for transmission of hybrid-ARQ acknowledgements inresponse to downlink scheduling assignments. The DCI also includesuplink scheduling grants, including PUSCH resource indication, transportformat, and hybrid-ARQ-related information. An uplink scheduling grantalso includes a command for power control of the PUSCH. The DCI alsoincludes power-control commands for a set of terminals as a complementto the commands included in the scheduling assignments/grants.

One PDCCH/EPDCCH carries one DCI message containing one of the groups ofinformation listed above. As multiple terminals can be scheduledsimultaneously, and each terminal can be scheduled on both downlink anduplink simultaneously, it should be possible to transmit multiplescheduling messages within each subframe. Each scheduling message istransmitted on separate PDCCH/EPDCCH resources, and consequently thereare typically multiple simultaneous PDCCH/EPDCCH transmissions withineach subframe in each cell. Furthermore, to support differentradio-channel conditions, link adaptation can be used, where the coderate of the PDCCH/EPDCCH is selected by adapting the resource usage forthe PDCCH/EPDCCH, to match the radio-channel conditions.

In LTE, the uplink (UL) transmission scheduling command is transmittedfrom the eNB to the user equipment (UE). There is a fixed delay betweenthe time the scheduling command is transmitted and the time the UEtransmits the UL signal specified in the standard. This delay isprovisioned to allow the UE time to decode the PDCCH/EPDCCH and preparethe UL signal for transmission. For a frequency division duplex (FDD)serving cell, this UL grant delay is 4 ms. For a time division duplex(TDD) serving cell, this UL grant can be greater than 4 ms.

Carrier Aggregation

The LTE Rel-10 standard supports bandwidths larger than 20 MHz. Oneimportant requirement on LTE Rel-10 is to assure backward compatibilitywith LTE Rel-8. This should also include spectrum compatibility. Thatwould imply that an LTE Rel-10 carrier, wider than 20 MHz, should appearas a number of LTE carriers to an LTE Rel-8 terminal. Each such carriercan be referred to as a Component Carrier (CC). In particular, for earlyLTE Rel-10 deployments it can be expected that there will be a smallernumber of LTE Rel-10-capable terminals compared to many LTE legacyterminals. Therefore, it is necessary to assure an efficient use of awide carrier also for legacy terminals, i.e., that it is possible toimplement carriers where legacy terminals can be scheduled in all partsof the wideband LTE Rel-10 carrier. The straightforward way to obtainthis would be by means of Carrier Aggregation (CA). CA implies that anLTE Rel-10 terminal can receive multiple CCs, where the CCs have, or atleast the possibility to have, the same structure as a Rel-8 carrier. Anexample of CA is illustrated in FIG. 4. A CA-capable UE is assigned aprimary cell (PCell) which is always activated, and one or moresecondary cells (SCells) which may be activated or deactivateddynamically.

The number of aggregated CCs, as well as the bandwidth of the individualCC, may be different for uplink and downlink. A symmetric configurationrefers to the case where the number of CCs in downlink and uplink is thesame, whereas an asymmetric configuration refers to case where thenumber of CCs is different. It is important to note that the number ofCCs configured in a cell may be different from the number of CCs seen bya terminal. A terminal may for example support more downlink CCs thanuplink CCs, even though the cell is configured with the same number ofuplink and downlink CCs.

In addition, a key feature of carrier aggregation is the ability toperform cross-carrier scheduling. This mechanism allows an (E)PDCCH onone CC to schedule data transmissions on another CC by means of a 3-bitCIF inserted at the beginning of the (E)PDCCH messages. For datatransmissions on a given CC, a UE expects to receive scheduling messageson the (E)PDCCH on just one CC—either the same CC, or a different CC viacross-carrier scheduling; this mapping from (E)PDCCH to PDSCH is alsoconfigured semi-statically.

In LTE, the scheduling information of DL and UL transmission on thePCell is transmitted on the PCell using PDCCH or EPDCCH. This basicscheduling mechanism is referred to as the self-scheduling method inLTE. For a SCell, two scheduling mechanisms are supported: SCellself-scheduling and SCell cross-carrier scheduling. For SCellself-scheduling, as in the case of the PCell, the scheduling informationof DL and UL transmission on the SCell is transmitted on the same SCellitself using PDCCH or EPDCCH. For SCell cross-carrier scheduling, thenetwork can also configure a SCell via higher layer signaling to use across-carrier scheduling mechanism. In this approach, the schedulinginformation of DL and UL transmission on a SCell is transmitted on asecond cell using PDCCH or EPDCCH. Said second cell can be the PCell oranother SCell.

Note, for LTE, the DL and UL scheduling approaches are configuredtogether. That is, the DL and UL transmissions of a cell are either bothself-scheduling or both cross-carrier scheduling.

Wireless Local Area Network

In typical deployments of wireless local area networks (WLANs), carriersense multiple access with collision avoidance (CSMA/CA) is used formedium access. This means that the channel is sensed to perform a clearchannel assessment (CCA), and a transmission is initiated only if thechannel is declared as Idle. In the event that the channel is declaredas Busy, the transmission is deferred until the channel is deemed to beIdle. When the range of several APs using the same frequency overlap,this means that all transmissions related to one AP might be deferred inthe event that a transmission on the same frequency to or from anotherAP that is within range can be detected. Effectively, this means that ifseveral APs are within range, they will have to share the channel intime, and the throughput for the individual APs may be severelydegraded. A general illustration of the LBT mechanism is shown in FIG.5.

After a Wi-Fi station A transmits a data frame to a station B, station Bshall transmit the ACK frame back to station A with a delay of 16 μs.Such an ACK frame is transmitted by station B without performing a LBToperation. To prevent another station interfering with such an ACK frametransmission, a station shall defer for a duration of 34 μs (referred toas distributed coordinated function (DCF) inter-frame space, or DIFS)after the channel is observed to be occupied before assessing againwhether the channel is occupied.

Therefore, a station that wishes to transmit first performs a CCA bysensing the medium for a fixed duration DIFS. If the medium is idle,then the station assumes that it may take ownership of the medium andbegin a frame exchange sequence. If the medium is busy, the stationwaits for the medium to go idle, defers for DIFS, and waits for afurther random backoff period.

To further prevent a station from occupying the channel continuously andthereby prevent other stations from accessing the channel, it isrequired for a station wishing to transmit again after a transmission iscompleted to perform a random backoff.

The point coordination function (PCF) inter-frame space (PIFS) is usedto gain priority access to the medium, and is shorter than the DIFSduration. Among other cases, it can be used by stations (STAs) operatingunder PCF, to transmit Beacon Frames with priority. At the nominalbeginning of each Contention-Free Period (CFP), the point coordinator(PC) shall sense the medium. When the medium is determined to be idlefor one PIFS period (generally 25 μs), the PC shall transmit a Beaconframe containing the CF Parameter Set element and a delivery trafficindication message element.

For a device not utilizing the Wi-Fi protocol, EN 301.893, v. 1.7.1provides the following requirements and minimum behavior for theload-based clear channel assessment. As a first requirement, before atransmission or a burst of transmissions on an Operating Channel, theequipment shall perform a CCA check using “energy detect”. The equipmentshall observe the Operating Channel(s) for the duration of the CCAobservation time, which shall be not less than 20 μs. The CCAobservation time used by the equipment shall be declared by themanufacturer. The Operating Channel shall be considered occupied if theenergy level in the channel exceeds the threshold corresponding to apower level. If the equipment finds the channel to be clear, it maytransmit immediately.

As a second requirement, if the equipment finds an Operating Channeloccupied, it shall not transmit in that channel The equipment shallperform an Extended CCA check in which the Operating Channel is observedfor the duration of a random factor N multiplied by the CCA observationtime. N defines the number of clear idle slots resulting in a total IdlePeriod that need to be observed before initiation of the transmission.The value of N shall be randomly selected in the range 1 . . . q everytime an Extended CCA is required and the value stored in a counter. Thevalue of q is selected by the manufacturer in the range 4 . . . 32. Thisselected value shall be declared by the manufacturer. The counter isdecremented every time a CCA slot is considered to be “unoccupied”. Whenthe counter reaches zero, the equipment may transmit. The equipment isallowed to continue Short Control Signalling Transmissions on thischannel providing it complies with the requirements in clause 4.9.2.3.For equipment having simultaneous transmissions on multiple (adjacent ornon-adjacent) operating channels, the equipment is allowed to continuetransmissions on other Operating Channels providing the CCA check didnot detect any signals on those channels.

As a third requirement, the total time that an equipment makes use of anOperating Channel is the Maximum Channel Occupancy Time which shall beless than (13/32)×q ms, with q as defined for the second requirement,after which the device shall perform the Extended CCA.

As a fourth requirement, the equipment, upon correct reception of apacket which was intended for this equipment, can skip CCA andimmediately proceed with the transmission of management and controlframes (e.g. ACK and Block ACK frames). A consecutive sequence oftransmissions by the equipment, without it performing a new CCA, shallnot exceed the Maximum Channel Occupancy Time as defined for the thirdrequirement. For the purpose of multi-cast, the ACK transmissions(associated with the same data packet) of the individual devices areallowed to take place in a sequence.

As a fifth requirement, the energy detection threshold for the CCA shallbe proportional to the maximum transmit power (PH) of the transmitter:for a 23 dBm e.i.r.p. transmitter the CCA threshold level (TL) shall beequal or lower than −73 dBm/MHz at the input to the receiver (assuming a0 dBi receive antenna). For other transmit power levels, the CCAthreshold level TL shall be calculated using the formula: TL=−73dBm/MHz+23−PH (assuming a 0 dBi receive antenna and PH specified in dBme.i.r.p.). An example illustrating the LBT procedure in EN 301.893 isprovided in FIG. 6.

Up to now, the spectrum used by LTE is dedicated to LTE. This has theadvantage that an LTE system does not need to care about coexistencewith other non-3GPP radio access technologies in the same spectrum andspectrum efficiency can be maximized However, the spectrum allocated toLTE is limited and cannot meet the ever increasing demand for largerthroughput from applications/services. Therefore, a new study item hasbeen initiated in 3GPP on extending LTE to exploit unlicensed spectrumin addition to licensed spectrum.

With Licensed-Assisted Access (LAA) to unlicensed spectrum, as shown inFIG. 7, a UE is connected to a PCell in the licensed band and one ormore SCells in the unlicensed band. In this application, the secondarycell in unlicensed spectrum is denoted as an LAA secondary cell (LAASCell). The LAA SCell may operate in DL-only mode or operate with bothUL and DL traffic. Furthermore, in future scenarios the LTE nodes mayoperate in standalone mode in license-exempt channels without assistancefrom a licensed cell. Unlicensed spectrum can, by definition, besimultaneously used by multiple different technologies. Therefore, LAAas described above needs to consider coexistence with other systems suchas IEEE 802.11 (Wi-Fi).

To coexist fairly with the Wi-Fi system, transmission on the SCell shallconform to LBT protocols in order to avoid collisions and causing severeinterference to on-going transmissions. This includes both performingLBT before commencing transmissions, and limiting the maximum durationof a single transmission burst. The maximum transmission burst durationis specified by country and region-specific regulations. For example,the maximum burst duration is 4 ms in Japan and 13 ms according to EN301.893. An example in the context of LAA is shown in FIG. 8 withdifferent examples for the duration of a transmission burst on the LAASCell constrained by a maximum allowed transmission duration of 4 ms.

There are two possible approaches to support UL transmission on an LAASCell. In a first approach, the UE follows an LBT protocol to attemptchannel access after receiving the UL transmission scheduling command.This is illustrated in an example of 4 ms channel occupancy time systemin FIG. 9. That is, the LBT protocol is designed to allow 4 ms DLchannel occupancy time and 4 ms UL channel occupancy time. In a secondapproach, the UE does not follow any LBT protocol to initiate channelaccess after receiving the UL transmission scheduling command This isillustrated for an example of 8 ms channel occupancy time system in FIG.10. In this example, the LBT protocol is designed to allow 8 ms totalchannel occupancy time between DL and UL transmissions. LBT and CCA areperformed by the eNB before the start of DL transmissions.

SUMMARY

There is a need in the art for improved mechanisms for scheduling, forexample in cells configured on a carrier where an LBT protocol isrequired to be used for transmission, and in cells configured oncarriers where uplink transmissions should follow a reverse directiongrant protocol.

A first problem exists where UL transmissions follow an LBT protocol.Following the current LTE scheduling configuration specs, the DL and ULtransmissions on an LAA SCell will both follow either self-scheduling orcross-carrier scheduling. This restriction can severely limit theoperation and performance of LAA under certain operation conditions. Acongested scenario can arise when there are many nodes contending toaccess the channel, such as when the LAA system is operating on the samefrequency as another Wi-Fi network with many UEs. Suppose there are Nnodes, including small cells (such as LAA eNBs or Wi-Fi APs) and UEs,contending for channel access. There is then a 1/N chance that an LAAeNB can obtain the channel access, in which it can transmit theself-scheduling information to schedule UL transmission from itsassociated UEs. The UEs, upon receiving the UL transmission schedulingcommand, will try to access the channel following an LBT protocol, whichby itself gives the UE a 1/N chance of obtaining the channel. However,the UE's LBT action is contingent on receiving the scheduling commandfrom the eNB, which requires the eNB obtaining the channel in the firstplace. That is, the net probability of a successful UL transmission isclose to 1/N². When there are a large number of nodes operating in thesame frequency, this analysis shows the LAA UL operation will notfunction well.

A second problem occurs when UL transmissions follow a reverse directiongrant protocol. In some regions, the maximum allowed channel occupancytime may be very short. For example, the Japanese regulation limits thechannel occupancy time to 4 ms. This will prevent the use of reversedirection grant protocol for UL transmission since the UL grant delay isat least 4 ms.

An advantage of some of the proposed solutions is enhanced LAA ULtransmission operations. Two operations are proposed to enable betterLAA UL transmissions. To address problem 1, scheduling methods for DLtransmission and UL transmission can be configured separately. Toaddress problem 2, a reverse direction grant assistance signal istransmitted in the DL to enable UL reverse direction grant protocoloperations.

According to some embodiments, a method is performed at a wirelessdevice that is connected to a first cell and a second cell, where thesecond cell is configured on a carrier where a LBT protocol fortransmission is required to be used. The method includes receiving aconfiguration message indicating that downlink transmissions on thesecond cell are to be scheduled. Downlink transmissions may be scheduledusing self-scheduling on the second cell, and that uplink transmissionson the second cell are to be scheduled using cross-carrier scheduling onthe first cell. For self-scheduling, the scheduling command and data aresent on the same cell. With cross-carrier scheduling, the schedulingcommand and the data are sent on different cells. It is also possiblethat two separate configuration messages are received, one for thedownlink and one for the uplink. The configuration message or messagesmay be transmitted via radio resource control (RRC) signalling. Themethod includes receiving a scheduling grant in the first cell. Themethod also includes, in a subframe occurring a predetermined number ofsubframes after receiving the scheduling grant, performing a CCA in thesecond cell. The method includes transmitting an uplink messageresponsive to success of the CCA.

According to some embodiments, a method performed at a network node thatserves a first cell and a second cell, where the second cell isconfigured on a carrier where an LBT protocol for transmission isrequired to be used, includes transmitting, to a wireless device, one ormore configuration messages indicating that downlink transmissions onthe second cell are to be scheduled. Downlink transmissions may bescheduled using self-scheduling on the second cell, and that uplinktransmissions on the second cell are to be scheduled using cross-carrierscheduling on the first cell. It is equally possible to transmit twoseparate configuration messages, one for the downlink transmission andone for the uplink transmissions. Further, the method includestransmitting a scheduling grant to the wireless device in the firstcell. Advantageously, in the first cell, it is not required to use LBT.For instance, the first cell may be operating on LTE licensed spectrum.Thus, the network node may transmit the scheduling grant without firstperforming a CCA. Subsequent to transmitting the scheduling grant, themethod includes receiving an uplink message from the wireless device inthe second cell according to the transmitted scheduling grant.

According to some embodiments, a method performed at a network nodeserving a first cell and a second cell, where the second cell isconfigured on a carrier where an LBT protocol for transmission isrequired to be used, includes transmitting, to a wireless device, one ormore configuration messages indicating that downlink transmissions onthe second cell are to be scheduled using self-scheduling on the secondcell, and that uplink transmissions on the second cell are to bescheduled using cross-carrier scheduling on the first cell. The methodalso includes transmitting a scheduling grant to the wireless device inthe first cell and receiving an uplink message from the wireless devicein the second cell, according to the transmitted scheduling grant.

According to some embodiments, a method performed at a wireless deviceconnected to a cell operated by a network node (e.g., base station),where the cell is configured on a carrier where an LBT protocol fortransmission is required to be used, includes receiving a schedulinggrant from the network node. The method also includes receiving, fromthe network node, a grant confirmation signal indicating that thenetwork node has performed a CCA on the carrier and is releasing thecarrier for the wireless device. The method further includes responsiveto receiving the scheduling grant and the grant confirmation signal,transmitting an uplink message on the carrier without performing a CCAon the carrier.

According to some embodiments, a method performed at a network nodeserving a cell, where the cell is configured on a carrier where an LBTprotocol for transmission is required to be used and where at least onewireless device is connected to the cell, includes transmitting ascheduling grant to a wireless device for the carrier, for a scheduleduplink transmission. The method also includes performing a first CCA forthe carrier, prior to a time for the scheduled uplink transmission and,responsive to success of the CCA, transmitting a grant confirmationsignal to the wireless device and releasing the carrier for thescheduled uplink transmission.

The method may also be implemented by wireless devices, network nodes,computer readable medium, computer program products and functionalimplementations.

Of course, the present invention is not limited to the above featuresand advantages. Those of ordinary skill in the art will recognizeadditional features and advantages upon reading the following detaileddescription, and upon viewing the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the LTE downlink physical resource.

FIG. 2 illustrates an LTE time-domain structure.

FIG. 3 illustrates a normal downlink subframe.

FIG. 4 illustrates carrier aggregation.

FIG. 5 is a diagram illustrating LBT in Wi-Fi.

FIG. 6 is a diagram illustrating LBT in EN 301.893.

FIG. 7 illustrates a CA-capable UE configured with an LAA SCell.

FIG. 8 is a diagram illustrating LAA to unlicensed spectrum using LTE CAand LBT.

FIG. 9 is a diagram illustrating UL LAA transmissions based on an UL LBTprotocol.

FIG. 10 is a diagram illustrating UL LAA transmissions based on areverse direction grant protocol.

FIG. 11 is a flowchart illustrating a method in a wireless device fortransmission using CCA, according to some embodiments.

FIG. 12 is a flowchart illustrating a method in a network node forscheduling transmission, according to some embodiments.

FIG. 13 is a diagram illustrating UL LAA transmissions based on areverse direction grant protocol with an assisting DL indication.

FIG. 14 is a flowchart illustrating a method in a network node forscheduling using CCA, according to some embodiments.

FIG. 15 is a flowchart illustrating a method in a wireless device fortransmission, according to some embodiments.

FIG. 16 illustrates an LTE network that uses CA in which someembodiments may be implemented.

FIG. 17 illustrates a block diagram of a wireless device configured toperform related methods, according to some embodiments.

FIG. 18 illustrates a block diagram of a network node configured toperform related methods, according to some embodiments.

FIG. 19 is a diagram illustrating an embodiment of DL-only LAA SCellself-scheduling.

FIG. 20 is a diagram illustrating an embodiment of UL+DL LAA SCellself-scheduling.

FIG. 21 is a diagram illustrating an embodiment of DL-only LAAcross-carrier scheduling based on PDCCH.

FIG. 22 is a diagram illustrating an embodiment of DL-only LAAcross-carrier scheduling based on EPDCCH.

FIG. 23 is a diagram illustrating an embodiment of DL-only LAAcross-carrier scheduling based on EPDCCH.

FIG. 24 is a diagram illustrating an embodiment of UL+DL basedcross-carrier scheduling based on EPDCCH.

FIG. 25 is a diagram illustrating an embodiment of UL+DL basedcross-carrier scheduling based on EPDCCH with a TDD scheduling cell.

FIG. 26 is a flowchart illustrating an overview of an example LBTprocedure for LAA.

FIG. 27 is a diagram illustrating an example of an LBT protocol with orwithout freeze periods in a medium load scenario.

FIG. 28 is a diagram illustrating an example of an LBT protocol with orwithout freeze periods in a heavily occupied medium.

FIG. 29 is a diagram illustrating examples of LAA self-scheduling on theSCell with maximum channel occupancy of 4 ms.

FIG. 30 is a diagram illustrating an examples of freeze periods tosupport different TMs.

FIG. 31 is a flowchart illustrating an example LBT for management andcontrol information.

FIG. 32 illustrates an example functional implementation of a wirelessdevice, according to some embodiments.

FIG. 33 illustrates an example functional implementation of a networknode, according to some embodiments.

FIG. 34 illustrates another example functional implementation of awireless device, according to some embodiments.

FIG. 35 illustrates another example functional implementation of anetwork node, according to some embodiments.

DETAILED DESCRIPTION

Although this disclosure refers to “licensed” and “unlicensed” spectrum,it should be noted that this is only an illustrative scenario and shouldnot be construed as limiting. For example, what is referred to in thisdisclosure as “unlicensed” spectrum could be licensed but still madeavailable for use under certain conditions (for instance, during certaintime periods, or when no users that have priority access to the spectrumare present in the cell). This is sometimes referred to as “LicenseShared Access” or LSA. Moreover, unless otherwise specified herein, itis not essential to the solution whether a certain spectrum is actually“licensed” or not. The solutions may be applicable in general inscenarios where spectrum in a cell is shared with other radiotechnologies, especially when those technologies employ differentprotocols for gaining channel access, and/or different protocols forscheduling.

Further, in the context of this disclosure, CCA encompasses anytechnique for detecting whether the channel is not being used, before atransmission is performed. The assessment may be limited to specificresources, but it may also require CCA to be performed over a widerbandwidth, for example the full bandwidth of a cell. Thus, an LBTprotocol, as discussed herein, involves, on a general level, performinga CCA, and then transmitting only when the CCA is successful, that is,transmitting when the channel is declared as not busy (or, equivalently,declared as idle). The CCA may in some cases be performed on behalf ofanother device. For example, in a “reverse direction grant protocol”, anetwork node (e.g., a base station or Wi-Fi access point) may performCCA to secure the channel for a subsequent uplink transmission by awireless device.

In a first embodiment, scheduling methods for DL transmission and ULtransmission can be configured separately via higher layer signaling. Anon-limiting example of said higher layer signaling is the RRC layersignaling in LTE. For example, DL transmission is configured to followself-scheduling and UL transmission is configured to followcross-carrier scheduling. For the LAA use case, if the UL transmissionis cross-scheduled from a cell not following LBT protocol (for example,the PCell in the licensed band), the UL transmission attempts will besubject to only one LBT procedure (instead of two LBT procedures. Forexample, in the self-scheduling case where the eNB has to perform LBTbefore sending he scheduling message, followed by the UE performing anLBT before sending the scheduled data. This embodiment will allow theLAA UL transmission to perform well even in congested scenarios.

An example embodiment in a wireless device will now be described withreference to the flowchart in FIG. 11 below. FIG. 11 illustrates amethod 1100 performed at a wireless device. The wireless device isconnected to a first cell and a second cell, wherein the second cell isconfigured on a carrier where an LBT protocol for transmission isrequired to be used. The method 1100 includes receiving a configurationmessage indicating that downlink transmissions on the second cell are tobe scheduled (block 1102). Downlink transmissions may be scheduled usingself-scheduling on the second cell, and that uplink transmissions on thesecond cell are to be scheduled using cross-carrier scheduling on thefirst cell. It is also possible that two separate configuration messagesare received, one for the downlink and one for the uplink. Theconfiguration message or messages may be transmitted via radio resourcecontrol (RRC) signalling. The method 1100 includes receiving ascheduling grant in the first cell (block 1104). The method 1100includes, in a subframe occurring a predetermined number of subframesafter receiving the scheduling grant, performing a clear channelassessment in the second cell (block 1106). The method 1100 includestransmitting an uplink message responsive to success of the clearchannel assessment (block 1108).

In some variants, the wireless device is configured with carrieraggregation, and the first cell is the configured PCell, and the secondcell is a configured SCell. The second cell may be configured on carrierthat is shared with other radio technologies such as Wi-Fi. The carriermay use unlicensed spectrum.

An example embodiment in a network node, e.g., an LTE base station, willnow be described with reference to the flowchart in FIG. 12. The method1200 is performed at the network node that serves a first cell and asecond cell, where the second cell is configured on a carrier where anLBT protocol for transmission is required to be used. The method 1200includes transmitting, to a wireless device, one or more configurationmessages indicating that downlink transmissions on the second cell areto be scheduled (block 1202). Downlink transmissions may be scheduledusing self-scheduling on the second cell, and that uplink transmissionson the second cell are to be scheduled using cross-carrier scheduling onthe first cell. It is equally possible to transmit two separateconfiguration messages, one for the downlink transmission and one forthe uplink transmissions. Further, the method 1200 includes transmittinga scheduling grant to the wireless device in the first cell (block1204). Advantageously, in the first cell, it is not required to use LBT.For instance, the first cell may be operating on LTE licensed spectrum.Thus, the network node may transmit the scheduling grant without firstperforming a CCA. Subsequent to transmitting the scheduling grant, themethod 1200 includes receiving an uplink message from the wirelessdevice in the second cell according to the transmitted scheduling grant(block 1206).

In a second embodiment, an assisting signal is transmitted in the DL toassist the operation of UL reverse direction grant protocol. Thisembodiment is to address the situation where the allowed channeloccupancy time is not long enough to enable effective operation of theUL reverse direction grant protocol. In this example, the UE detects thereverse direction grant assistance signal before transmitting the ULwithout LBT.

Thus, the “reverse direction grant protocol” implies that the networknode (e.g., a base station) performs CCA to secure channel access forthe UE, so that the UE does not need to perform CCA before transmittingin the uplink. In some embodiments, the reverse direction grantassistance signal is a PDCCH or an EPDCCH. In other embodiments, thereverse direction grant assistance signal is a sequence of symbolstransmitted in specific time-frequency locations known to the UE (suchas the CRS). In some examples, the reverse direction grant assistancesignal is a dedicated physical channel specifically defined for carryingsaid information. An example of such a dedicated physical channel is thephysical hybrid-ARQ indicator channel (PHICH) in LTE.

In some embodiments, the reverse direction grant assistance signalconveys the number of subframes for which the channel access has beengained. Such information can be provided by signaling the number ofsubframes after the subframe in which the grant assistance signal occursfor which channel access is secured.

In an example, a UE is provided with location information of the reversedirection grant assistance signal within the frame structure. In anexample implementation, this information is the number of subframesrelative to the UL scheduling command In the example illustration inFIG. 13, the UL transmission command in subframe n−4 contains a +3 indexinformation, indicating the UE shall detect the reverse direction grantassistance signal in subframe n−1 before transmitting the UL withoutLBT.

In a second example, the location of the reverse direction grantassistance signal is known to UE. In a first example implementation, thelocation information is fixed in the standard specification. In a secondexample implementation, the location information is configured viahigher layer signaling and becomes fixed for the serving cell until areconfiguration.

In a third example, the reverse direction grant assistance signal, sentusing any of the above methods, carries information for multiple ULSCells on which the UE can transmit without LBT.

In a fourth example, the reverse direction grant assistance signal issent to the UE on a licensed PCell or SCell, along with associated CIFinformation to indicate the corresponding UL SCell. The “reversedirection grant assistance signal” is, throughout this disclosure,alternatively referred to as a “grant confirmation signal.”

In another example, a network node serves a cell, wherein the cell isconfigured on a carrier where an LBT protocol for transmission isrequired to be used. At least one wireless device is connected to thecell. This method includes performing a CCA, and transmitting ascheduling grant to a wireless device when the CCA is successful. Thenetwork node then performs a second CCA and, when the second CCA issuccessful, it transmits a grant confirmation signal to the wirelessdevice.

The second CCA may be performed a certain number of subframes (e.g., 3subframes) after transmitting the scheduling grant. Thereby, channelaccess is secured for additional subframes, which is advantageous if thecell is configured on spectrum where the channel occupancy time islimited (for example, limited to 4 subframes). The grant confirmationsignal may, in some variants, be transmitted shortly after the secondCCA has succeeded, for example, in the following subframe.

The wireless device waits until it receives the grant confirmationsignal before it actually performs a scheduled uplink transmission.Hence, the network node may receive an uplink transmission subsequent totransmitting the grant confirmation signal.

Advantageously, the network node may send scheduling grants to severalwireless devices, and the second CCA may then be used to secure channelaccess for all these scheduled devices. Thereby, it is not necessary foreach wireless device to perform a separate CCA before an uplinktransmission. If each wireless device were to perform a separate CCA,the devices might interfere with each other, because the CCAs are likelyto complete at slightly different times. Thus, if a first device hasperformed a successful CCA and started to transmit, the transmissionfrom the first device might prevent a second device from obtainingchannel access.

FIG. 14 illustrates another method 1400 performed by a network node. Themethod 1400 includes transmitting a scheduling grant to a wirelessdevice for the carrier, for a scheduled uplink transmission (block1402), and performing a first CCA for the carrier, prior to a time forthe scheduled uplink transmission (block 1404). The transmitting of thescheduling grant may be preceded by performing a second CCA for thecarrier. The first CCA may be performed a predetermined number ofsubframes after transmitting the scheduling grant. In some cases, thepredetermined number of subframes is three.

The method 1400 also includes, responsive to success of the first CCA,transmitting a grant confirmation signal to the wireless device andreleasing the carrier for the scheduled uplink transmission (block1406). The grant confirmation signal may comprise an indication of thenumber of subframes for which channel access has been secured.

In some cases, scheduling grants may be transmitted to each of more thanone wireless device responsive to the first CCA being successful. Insome cases, the method 1400 includes scheduling all of the more than onewireless devices in each of every subframe for which channel access hasbeen secured by performing the first CCA and releasing the carrier. Inother cases, the method 1400 includes scheduling at least one wirelessdevice for fewer than all of the subframes in a series of subframes forwhich channel access has been secured by performing the first CCA andreleasing the carrier, where the grant confirmation signal transmittedto the at least one wireless device indicates the number of subframesfor which channel access has been secured.

The method 1400 may include receiving an uplink transmission from thewireless device after transmitting the grant confirmation signal. Theuplink transmission may be received in the subframe immediatelyfollowing a subframe in which the grant confirmation signal wastransmitted.

In another example, a wireless device is connected to a cell, whereinthe cell is configured on a carrier where an LBT protocol fortransmission is required to be used. The method comprises receiving ascheduling grant, and subsequently receiving a grant confirmationsignal. Responsive to receiving the grant confirmation signal, thewireless device transmits an uplink message. The grant confirmationsignal indicates to the wireless device that channel access has beensecured. Thus, the wireless device does not need to perform CCA beforetransmitting the uplink message. As mentioned above, the network nodehas already performed the CCA before transmitting the grant confirmationsignal and thereby secured channel access for the device (and possiblyfor other devices as well).

FIG. 15 illustrates a method 1500 performed by a wireless device,according to some embodiments. The wireless device is connected to acell, wherein the cell is configured on a carrier where an LBT protocolfor transmission is required to be used. The method 1500 includesreceiving a scheduling grant from a network node (e.g., base station)(block 1502). The method 1500 also includes receiving, from the networknode, a grant confirmation signal indicating that the network node hasperformed a CCA on the carrier and is releasing the carrier for thewireless device (block 1504). The method 1500 further includes,responsive to receiving the scheduling grant and the grant confirmationsignal, transmitting an uplink message on the carrier without performinga CCA on the carrier (block 1506). The grant confirmation signal may bereceived in, or subsequent to, the subframe before the first scheduledsubframe according to the scheduling grant.

In a third embodiment, when the UL transmission burst consists ofmultiple subframes after the channel is accessed and before the channelis released, all the UEs that are scheduled for UL transmissions in oneburst are scheduled so that every UE is scheduled in each of thesubframes. This method of scheduling can be combined with the reversegrant assistance signal in the previous embodiment where the signal isprovided a certain number of subframes after the scheduling command isreceived by the UEs on the downlink as shown in FIG. 13. In this case,the grant assistance signal does not provide any information regardingthe number of subframes for which channel access is secured. It onlyindicates the binary information regarding whether channel access hasbeen secured or not. Each UE simply assumes that it can transmit in allsubframes for which it has been scheduled.

In some embodiments, the UL transmissions for multiple UEs may bescheduled so that not all UEs transmit in all subframes in thetransmission burst. In this case, for example, a particular UE may notbe scheduled in the very first UL subframe of the transmitted burst.This method of scheduling UEs is then coupled with the embodiment wherethe reverse direction grant assistance signal indicates the number ofsubframes for which the channel access has been secured. Using thisinformation, along with the scheduling information, allows the UE todetermine whether it can transmit in a particular scheduled subframewithout performing any LBT operation.

As for a fourth embodiment, cross-carrier scheduling based on EPDCCH isconsidered. For EPDCCH, it may be possible to avoid the case whereEPDCCH is needed to be provided before or at the same time as thecorresponding PDSCH. This is by configuring the EPDCCH to start later inthe subframe than the PDSCH would start on the LAA SCell. However, theeNB would need to have completed the processing of the time domainsignal to be transmitted soon within 1 OFDM symbol or similar timingrelations before the EPDCCH is actually transmitted. However, it may bepossible that the eNB creates two different time domains samples, i.e.one with the EPDCCH included and one excluding the EPDCCH. Then eNB canthen choose the applicable OFDM symbol(s), the ones including EPDCCH orthe ones excluding EPDCCH. Based on whether or not the PDSCH on the LAASCell is transmitted. This problem occurs as soon as the eNB has toperform LBT for the LAA SCell.

Although the described solutions may be implemented in any appropriatetype of telecommunication system supporting any suitable communicationstandards and using any suitable components, particular embodiments ofthe described solutions may be implemented in an LTE network usingcarrier aggregation, such as that illustrated in FIG. 16. Embodimentsmay also be implemented in a 5G network.

As shown in FIG. 16, the example network may include one or moreinstances of wireless communication devices (e.g., conventional userequipment (UEs), machine type communication (MTC)/machine-to-machine(M2M) UEs) and one or more radio access nodes (e.g., eNodeBs or otherbase stations) capable of communicating with these wirelesscommunication devices along with any additional elements suitable tosupport communication between wireless communication devices or betweena wireless communication device and another communication device (suchas a landline telephone). Although the illustrated wirelesscommunication devices may represent communication devices that includeany suitable combination of hardware and/or software, these wirelesscommunication devices may, in particular embodiments, represent devicessuch as the example wireless communication device illustrated in greaterdetail by FIG. 17. Similarly, although the illustrated radio access nodemay represent network nodes that include any suitable combination ofhardware and/or software, these nodes may, in particular embodiments,represent devices such as the example radio access node illustrated ingreater detail by FIG. 18. Note also that although FIG. 16 shows anetwork node serving two cells, it is possible that one or both cellsare served by a remote radio unit (RRU) connected to the radio node. Itmay also be possible that the two cells shown in FIG. 16 are served byseparate network nodes, which are in communication with each other.

As shown in FIG. 17, the example wireless communication device 1700includes processor(s) 1720, a memory 1730, radio circuitry 1710 and anantenna. In particular embodiments, some or all of the functionalitydescribed above as being provided by UEs, MTC or M2M devices, and/or anyother types of wireless communication devices may be provided by theprocessor(s) 1720 executing instructions stored on a computer-readablemedium, such as the memory 1730 shown in FIG. 17; the combination of theprocessor(s) 1720 and memory 1730 may be referred to collectively as“processing circuitry.” Alternative embodiments of the wirelesscommunication device 1700 may include additional components beyond thoseshown in FIG. 17 that may be responsible for providing certain aspectsof the device's functionality, including any of the functionalitydescribed above and/or any functionality necessary to support thesolution described above.

According to some embodiments, the wireless device 1700 is configured tobe connectable to a first cell and a second cell, where the second cellis configured on a carrier where an LBT protocol for transmission isrequired to be used. The processing circuitry is configured to receiveone or more configuration messages, via the radio circuitry 1710,indicating that downlink transmissions on the second cell are to bescheduled. Downlink transmissions may be scheduled using self-schedulingon the second cell, and that uplink transmissions on the second cell areto be scheduled using cross-carrier scheduling on the first cell. Theprocessing circuitry is also configured to receive a scheduling grant inthe first cell and, in a subframe occurring a predetermined number ofsubframes after receiving the scheduling grant, perform a CCA in thesecond cell. The processing circuitry is configured to use the radiocircuitry 1710 to transmit an uplink message responsive to success ofthe CCA.

According to other embodiments, the wireless device 1700 is configuredto be connected to a cell operated by a network node (e.g., basestation) and configured to be connectable to a cell configured on acarrier where an LBT protocol for transmission is required to be used.The processing circuitry is configured to receive, via the radiocircuitry 1710, a scheduling grant from the network node and receive,from the network node, a grant confirmation signal indicating that thenetwork node has performed a CCA on the carrier and is releasing thecarrier for the wireless device 1700. The processing circuitry is alsoconfigured to, responsive to receiving the scheduling grant and thegrant confirmation signal, transmit an uplink message on the carrierwithout performing a CCA on the carrier.

As shown in FIG. 18, an example radio access node, such as network node1800, includes processor(s) 1820, a memory 1830, radio circuitry 1810,an antenna and a network interface 1840. In particular embodiments, someor all of the functionality described above as being provided by a basestation, a node B, an eNodeB, and/or any other type of network node maybe provided by the processor(s) 1820 executing instructions stored on acomputer-readable medium, such as the memory 1830 shown in FIG. 18; thecombination of processor(s) 1820 and memory 1830 may be collectivelyreferred to as processing circuitry. Alternative embodiments of theradio access node may include additional components responsible forproviding additional functionality, including any of the functionalityidentified above and/or any functionality necessary to support thesolution described above.

According to some embodiments, the network node 1800 is configured toserve a first cell and a second cell, where the second cell isconfigured on a carrier where an LBT protocol for transmission isrequired to be used. The processing circuitry is configured to transmit,to a wireless device 1700 via the radio circuitry 1810, one or moreconfiguration messages indicating that downlink transmissions on thesecond cell are to be scheduled. Downlink transmissions may be scheduledusing self-scheduling on the second cell, and that uplink transmissionson the second cell are to be scheduled using cross-carrier scheduling onthe first cell. The processing circuitry is also configured to transmita scheduling grant to the wireless device 1700 in the first cell andreceive an uplink message from the wireless device 1700 in the secondcell, according to the transmitted scheduling grant.

According to other embodiments, the processing circuitry of the networknode 1800 is configured to transmit a scheduling grant to a wirelessdevice for the carrier, via the radio circuitry 1810, for a scheduleduplink transmission and perform a first CCA for the carrier, prior to atime for the scheduled uplink transmission. The processing circuitry isalso configured to, responsive to success of the first CCA, transmit agrant confirmation signal to the wireless device and release the carrierfor the scheduled uplink transmission.

FIG. 32 illustrates an example functional module or circuit architectureas may be implemented in the wireless device 1700. The illustratedembodiment at least functionally includes a receiving module 3202 forreceiving one or more configuration messages indicating that downlinktransmissions on the second cell are to be scheduled. The receivingmodule (3202) is also for receiving a scheduling grant in the firstcell. The implementation also includes a performing module 3204 for, ina subframe occurring a predetermined number of subframes after receivingthe scheduling grant, performing a CCA in the second cell. Theimplementation also includes a transmitting module 3206 for transmittingan uplink message responsive to success of the CCA.

FIG. 33 illustrates an example functional module or circuit architectureas may be implemented in the network node 1800. The illustratedembodiment at least functionally includes a transmitting module 3302 fortransmitting, to a wireless device, one or more configuration messagesindicating that downlink transmissions on the second cell are to bescheduled. The transmitting module 3302 is also for transmitting ascheduling grant to the wireless device in the first cell. Theillustrated embodiment further includes a receiving module 3304 forreceiving an uplink message from the wireless device in the second cell,according to the transmitted scheduling grant.

FIG. 34 illustrates another example functional module or circuitarchitecture as may be implemented in the wireless device 1700. Theillustrated embodiment at least functionally a receiving module 3402 forreceiving a scheduling grant from a network node and for receiving, fromthe network node, a grant confirmation signal indicating that thenetwork node has performed a CCA on the carrier and is releasing thecarrier for the wireless device. The implementation also includes atransmitting module 3404 for, responsive to receiving the schedulinggrant and the grant confirmation signal, transmitting an uplink messageon the carrier without performing a CCA on the carrier.

FIG. 33 illustrates another example functional module or circuitarchitecture as may be implemented in the network node 1800. Theillustrated embodiment at least functionally includes a transmittingmodule 3502 for transmitting a scheduling grant to a wireless device forthe carrier, for a scheduled uplink transmission. The implementationalso includes a performing module 3504 for performing a first CCA forthe carrier, prior to a time for the scheduled uplink transmission. Thetransmitting module 3502 is also for, responsive to success of the firstCCA, transmitting a grant confirmation signal to the wireless device andreleasing the carrier for the scheduled uplink transmission.

Example Solutions

According to some embodiments, certain aspects could be implementedwithin the framework of a specific communication standard. Specifically,changes could be made to one or more of the 3GPP specifications 3GPP TS36.211 V11.4.0, 36.213 V11.4.0 and 36.331 V11.5.0, which methods can beused to implement certain embodiments of the described solutions. Thefollowing examples are merely intended to illustrate how a particularembodiment could be implemented in a particular standard. However, theexample solutions could also be implemented in other suitable manners,both in the above mentioned specifications and in other specificationsor standards.

The LTE design supports, in general, two different schedulingapproaches: cross-carrier scheduling and self-scheduling. The supportedset of scheduling design needs some considerations for LAA SCell due tothe LBT requirements on an LAA SCell, which differs from the previousLTE designs. For example, in one embodiment, self-scheduling is used forDL and cross-carrier scheduling is used on UL. In another embodiment,cross-carrier scheduling is used on DL and self-scheduling is used onUL. An applicable design of self-scheduling will be described before anapplicable design for cross-carrier scheduling.

For the case of a DL-only LAA SCell that operates self-scheduling, theassumption is that the DCI message is provided by EPDCCH. If the UEfinds an applicable EPDCCH, it would know that it has been assigned aPDSCH within that subframe. On the eNB side, this type of operation israther straightforward, as either the eNB succeeds with its LBToperations or it does not. If the eNB succeeds with the LBT operation,the eNB transmits both EPDCCH and PDSCH. For subframes that do notrequire a new LBT procedure, the eNB simply transmits EPDCCH and PDSCH.The requirement to support this operation is that the eNB configures anEPDCCH that always starts, for example, three OFDM symbols into thesubframe. Moreover, it should be allowed for the PDSCH to start from thefirst OFDM symbol or with the same offset as the EPDCCH.

As shown in FIG. 19, one embodiment is that for DL-only, LAA SCellself-scheduling is based on EPDCCH. For the case when LAA SCell operatesboth UL+DL, the DL scheduling with above EPDCCH approach can be reused.For UL scheduling, however, some further consideration is needed. Thereason is that if the UL is scheduled from an LAA SCell that requires DLLBT at eNB, and if it is also so that the UL transmission on the UE siderequires UL LBT, the actual PUSCH transmission in this case requires twoLBT procedures. Another option is that only the eNB performs LBT, whichis due to the UE transmitting directly after the eNB or another UE. TheeNB can perform LBT and hold the channel for UEs within a maximumchannel occupancy time. The UE accesses the channel in the UL for theremaining subframes to transmit PUSCH. In Wi-Fi, Reverse Direction Grant(RDG) is used so that one STA could grant the channel to another STAwithin the transmit opportunity (TxOp).

A similar approach can be applied in LAA. The scheduling delay of 4 msin LAA may be used, or some other optimization for self-schedulingdesign for UL based on the impact on the LAA UL performance and/orassuming the similar applicable features for Wi-Fi.

In another embodiment illustrated by FIG. 20, for UL+DL LAA, DLscheduling is based on self-scheduling with EPDCCH. Also for UL+DL LAA,UL scheduling is based on self-scheduling with EPDCCH. Adjustment to theLBT procedure in UL may need to be done in case self-scheduling isoperated.

Regarding cross-carrier scheduling, it may be assumed that the LAA SCellis scheduled from a licensed carrier. An LAA SCell may also be scheduledfrom another LAA SCell. In the case of DL-only LAA SCell, there arebasically two different operational modes. The first is assuming thatthe PDCCH is used to schedule the LAA SCell and the second is thatEPDCCH is used to schedule the LAA SCell. Assuming that the PDCCH isused, there will be a potential issue in the first subframe of a TxOP.The reason is that the eNB would need to transmit the PDCCH eitherbefore or at the same time as the PDSCH starts to be transmitted towardsthe UE. Since LBT needs to be done on LAA SCell in the beginning of thefirst subframe of TxOP, it is uncertain whether PDSCH will betransmitted on LAA SCell when PDCCH is transmitted on PCell as shown inFIG. 21. The PDCCH can therefore not indicate whether or not the PDSCHis actually transmitted to the UE. The UE would therefore need toblindly detect the presence of the PDSCH on the LAA SCell based ondetecting some form of signal on the LAA SCell.

An example solution is that the UE detects the presence of the initialsignal, but this may require that the initial signal is transmitted longenough to allow a reliable detection at the UE side. Another alternativesolution is that some signal is embedded in the beginning of the firstPDSCH. The two last approaches have an issue with the scenario where theUE's ON duration of the discontinuous reception (DRX) procedure is notaligned with TxOP duration, and hence these two approaches are notpreferred from this perspective. Blind detection of the PDSCH may beperformed assuming a very low error rate to avoid corrupting the softbuffer. A DL may be cross-carrier scheduled from PDCCH on a carrieroperating on a carrier operated in licensed spectrum.

Cross-carrier scheduling may be based on EPDCCH. For EPDCCH, it may bepossible to avoid the case that EPDCCH needs be provided before or atthe same time as the corresponding PDSCH. This is done by configuringthe EPDCCH to start later in the subframe than the PDSCH would start onthe LAA SCell.

Another embodiment is illustrated by FIG. 22. There are some commonissues for both EPDCCH and PDCCH based on DL cross-carrier scheduling.The first issue is that when the scheduling carrier is operating TDD, itis not possible for all subframes on the LAA SCell to be scheduled. Thisis because that DL assignment is only applicable for the same subframein which the (E)PDCCH is transmitted. This will be an issue if only DLcross-scheduling is supported as there will be no defined way toschedule the unused subframes as shown in FIG. 23. Potentially,multi-subframe scheduling may resolve this. However, if it is so thatthe amount of licensed carriers is very limited and there is a largeamount of unlicensed carriers, there is a risk that the licensed carrierwill need to take a very large overhead for scheduling LAA SCells. Thismay impact the usability of LAA SCell, if for example, the schedulingcarrier on licensed spectrum is in a macro eNB which serves many UEs andoperates many LAA SCells. This latter problem may be solved by allowingcross-carrier scheduling from an LAA SCell to another LAA SCell,although there is no clear benefit with this compared to operating eachLAA SCell in DL-only with self-scheduling. DL cross-carrier schedulingmay impact severally the amount of schedulable subframes in case thescheduling cell is operating TDD. If there are many unlicensed LAA SCellthere together with using DL cross-carrier, there may be a problem withoverhead on the licensed carriers.

Cross-carrier scheduling from a carrier in licensed spectrum isconsidered for both DL and UL scheduling. Compared to DL basedcross-carrier scheduling, this is more straightforward, assuming thatthe amount of carriers in licensed spectrum are rather balanced comparedto the amount of carriers used in the unlicensed band. In addition, thescheduling cell is FDD. It would, in this instance, be possible to avoidthe case that both the eNB and UE would be required to do LBT, by simplyrelying on that the UE performs LBT before transmitting.

FIG. 24 illustrates another embodiment, where UL+DL based cross-carrierscheduling is based on EPDCCH. Assuming that the scheduling cell is FDDand that the amount of unlicensed spectrum used is rather balancedcompared to the amount of licensed spectrum, support cross-carrierscheduling for UL from either (E)PDCCH may be beneficial. There are somefurther aspects that need to be considered. If the scheduling cell wereoperating in TDD mode, there would be a need to support multi-subframescheduling for the UL in order to get an efficient operation. FIG. 25illustrates another embodiment, where UL+DL based cross-carrierscheduling is based on EPDCCH with a TDD scheduling cell. The abovelimitations with self-scheduling and cross-carrier scheduling may or maynot be solved by allowing cross-carrier scheduling between different LAASCell. In some cases, self-scheduling is supported on the same carrieras the UL message will be transmitted. Consequently, there is a need todefine an LBT procedure allows self-scheduling for both UL and DL forLAA to operate in a fair manner with Wi-Fi. If in addition cross-carrierscheduling is wished to be supported, a cross-carrier schedulingsolution may be for UL only while the DL is fully based onself-scheduling. In some cases, self-scheduling is based on EPDCCH forboth UL and DL for any number of aggregated unlicensed carriers. Inother cases, cross-carrier scheduling for UL from (E)PDCCH is supportedtogether with self-scheduling for DL. The cross-carrier scheduling mayalso be for if the scheduling cell is TDD.

In sum, various embodiments may include the following: 1) for DL-only,LAA SCell self-scheduling is based on EPDCCH; 2) for UL+DL LAA, DLscheduling is based on self-scheduling with EPDCCH; 3) for UL+DL LAA, ULscheduling is based on self-scheduling with EPDCCH; 4) self-schedulingis based on EPDCCH for both UL and DL for any number of aggregatedunlicensed carriers; and 5) cross-carrier scheduling for UL from(E)PDCCH is supported together with self-scheduling for DL.

Additional LAA Embodiments

In some embodiments, the following functionalities may be included, inaddition to the current LAA TR on the unlicensed band: radio resourcemanagement (RRM) measurement including cell identification; automaticgain control (AGC) setting; coarse synchronization; fine frequency/timeestimation for at least demodulation; and channel state information(CSI) measurement, including channel and interference. Rel-12 DRS can bethe starting point for at least RRM measurement including cellidentification.

PHY-layer solutions will be described for how to perform measurement andreporting of CSI for an LAA SCell, according to some embodiments. Froman LTE carrier aggregation perspective, all serving cells arecategorized as intra-frequency cells. In LAA, the unlicensed carrier candynamically be changed according to the channel selection process in theeNB. Also, the CRS on which the reference signal received power (RSRP)and reference signal received quality (RSRQ) are based on are sparse andfurther subjected to LBT. This will have an impact on the UE measurementperformance.

In Rel-12, RSRP and RSRQ measurements are supported for the discoverysignal, while there is no support of reference signal time difference(RSTD) and Rx-Tx time difference. The same measurements may be supportedfor measurements in Rel-13 as for Rel-12. Support of RSTD and Rx-Tx timedifference can be added later if location based services are needed forLAA.

In one embodiment, for LAA, support for RSTD and Rx-Tx time diff is notrequired. When a SCell is active, from a measurements point of view, itis subject to performance requirements as an intra-frequency cell withdiscovery signal. If a discovery signal is subject to LBT, the detectionof a new LAA cell can potentially take longer. The detection period of a20 MHz channel is 15 DMTC periods. It may be noted that theidentification of an LAA intra frequency cell can be potentially longerdue to LBT of the discovery signal.

The measurement performance between legacy LTE cells vs legacy LTE cellswith discovery signal vs LAA cells with LBT will vary. It is likely thatsince the legacy LTE cells will be detected earlier and appears to bemore stable, they may be better candidates for SCell addition. Since thedecision of selecting an LAA cell is service based, algorithms forcomparing licensed vs unlicensed carrier operation may be considered.

RSRP and RSRQ measurements in the UE require positive identification andwill fail when LBT fails. Received signal strength indicator (RSSI)measurements on the other hand can always be measured by the UE. RSSImeasurements during an LBT failure on occasion can also be useful to theeNB. When tracked by the UE over a longer period of time, the eNB canget an idea of the other users on the carrier by using only themeasurements during LBT failures. Such information can be used for thelonger term channel selection. In order to distinguish between RSSI fromLBT failure occasions and RSSI from LBT success occasions, twoapproaches are possible. The first approach would be that the UE detectsLBT success/failure and tags the RSSI report with the correspondingdetection result. In the second approach, the UE simply reports RSSItogether with a potential time-stamp so that the eNB can keep track ofand filter the reports based on its LBT history.

In an embodiment, RSSI measurements are reported to the eNB regardlessof whether LBT detection showed success or failure. The UE could eithertag each report with the result from LBT detection or tag each reportwith a time stamp. With the latter option the eNB can keep track of thereports and filter them based on its LBT history. The discovery signalmay have gaps that give the opportunity for Wi-Fi to use the channel.

The following is a discussion on the types of information that can beconveyed in order to improve the system performance Network ID: Sincemultiple operators are sharing the same channel, the physical cellidentity is not sufficient identify the correct cell. The networkidentity may be transmitted on the discovery channel The UE may ensurethat this is decoded prior to performing any quality measurements.

In another embodiment, the Network-ID is included in the discoverysignal to enable the UE to correctly identify its own cell. As foroperating Carriers, an eNB may operate on several LAA carrierssimultaneously. If the eNB can send the LAA carriers on which it isoperating, other operator eNBs can use this information as input to itschannel selection. That is, if possible avoiding these particular LAAcarriers. As for carrier Usage, similarly, channel usage metrics for theoperating carriers may also be sent over the discovery signal to furtheraid another operator's eNBs for channel selection. This informationwould be even more useful when most LAA carriers are used and busy andmore detailed information of each channel is required. The point ofbroadcasting control information over the discovery signal is that thiscannot be done (for the above mentioned parameters) via the PCell.First, the dynamic changes in the parameters would cause an increase inthe X2 signalling load. Second, the PCell would have to be co-located.

In another embodiment, the operating carrier and carrier usage metricsare used in the discovery signal. Another parameter to considerbroadcasting over the discovery signal is the neighbor cell list. Thismay be a situation where the macro cell is containing many small LAAcells.

In sum, RRM measurements for an LAA SCell were discussed and based onthe discussion in the contribution, the following may be considered:since positioning features are not envisioned in this time frame,support for RSTD and Rx-Tx time diff is not required; RSSI measurementsare reported to the eNB; take action when a cell detection fails at theUE; include the Network-ID in the discovery signal to enable the UE tocorrectly identify its own cell; and consider including the operatingcarrier and carrier usage metrics in the discovery signal.

Further LAA Embodiments

Handling CSI measurements on LAA SCells needs to be handled with somecare. The CSI measurements may consist of two different measurementresources: CSI-RS and CSI-IM. The reason is that CSI measurementopportunities at the UE will be much more difficult to obtain whenoperating an LAA SCell because the eNB needs to perform LBT beforetransmitting CSI-RS. One embodiments includes extending the CSI-RSdesign so that the UE is configured to expect CSI-RS in a subframe or aset of subframes with a configured periodicity and offset. The eNB thenperforms LBT on CSI-RS and the UE would need to blindly detect thepresence of the CSI-RS. It is notable that it is very difficult to get agood blind decetion of a single CSI-RS resource. The risk of falselydetecting the presence of CSI-RS is large, i.e., the situation where theUE believes that the eNB has transmitted the CSI-RS but the eNB has not.It is noted that the presence of a specific CSI-RS needs to be indicatedto the UE.

Before further discussion on the different approaches on CSI-RStransmissions, the value of periodic and aperiodic CSI reports for LAASCells will be described. It is assumed that the interference conditionsmay be very varying on an LAA SCell over time. At the same time, thescenario that is considered is a very low mobility scenario. Theunderlying spatial properties and channel quality (if the interferenceconditions are excluded) is hence rather static over time. At the sametime, it is assumed that the LAA SCell will mainly be used to expand thedata rate, i.e., if the eNB has large amount of DL data to schedule toUE the eNB will utilise LAA SCells. Correspondlingly, the LAA SCell willbe used for significant time before the eNB has emptied its transmissionbuffer. Due to this, it is unlikely that the eNB will activate LAASCells without scheduling data on them for a long period of time.Periodic CSI reports are mainly used to get a good starting point forthe link adapation and scheduling and when data is being contintuouslyscheduled the resolution of the periodic CSI report is not good enough.This due to that the level of resolution in the periodic CSI feedback isnot good enough to provide reliable scheduling of high date rate. Inaddition, the reliable transmission of reference signals for CSI in aperiodic manner on the unlicensed band will not be possible due to apotential lack of access to the channel Due to all of the above reasonsthe most practical approach would be to rely only on aperiodic CSIreports for LAA SCell.

Accordingly, in some embodiments, LAA SCells do not support periodic CSIreports, but do support aperiodic CSI reports. Going back to the needfor the CSI-RS presence to be indicated to the UE, this needs to be donewith minimal delay as the eNB will decide in a very short time framewhether or not to transmit a specific set of subframe(s). It is possibleto introduce a specific indicator that indicates the presence of theCSI-RS, as for example, a specific DCI message that is scrambled withspecific radio network temporary identifier (RNTI) and indicates thepresence of a CSI reference signal (CSI-RS) on a specific carrier orgroup of carriers. This would require that the message is sent on asearch space that is common for many UEs, e.g. on Pcell. This togetherwith the DCI message could indicate which SCell the message applies toand potentially when in time.

In other embodiments, the presence of the CSI-RS is indicated to the UEreceiving the UL Grant which indicates that an aperiodic CSI messageshould be sent for the specific cell. In a case when the UL Grant issent on the SCell that the aperiodic CSI report is triggered for, it iseasy for the eNB to ensure that CSI-RS is transmitted together with theUL grant. If, however, the UL grant indicates an aperiodic CSI-RS reportfor a different cell than the one the UL grant is sent on, it may not bepossible to transmit CSI-RS in the very first subframe after the eNB hasoccupied the channel due to the very short processing time availablebetween the successful LBT on the carrier for which reporting is to bedone and the transmission time of the UL grant on a different carrier.If, however, the subframe is a later subframe within the eNB's TxOP, theeNB can have more processing time to indicate the presence of the CSI-RSon the SCell that the UL Grant is sent on.

The CSI-RS framework is a UE specific framework, i.e., a specific UE isnot aware of other UEs CSI-RS. Furthermore, the CSI-RS are configuredcurrently by a specific periodicity and offset. In addition there arethree CSI processes defined for CSI measurements.

Per CSI process, the UE would need to be configured with a rather shortperiodicity of CSI-RS as the eNB can not guarantee to succeed with LBTfor a longer periodicity based CSI-RS configuration. More specificallythere is a relationship between the TxOP used by the eNB and the CSI-RSconfiguration. If the periodicity of the CSI-RS can ensure that a singleCSI-RS occasion is within a TxOP that the eNB operates, the CSI-RS canoccur at any time occasion within the TxOP. If the CSI-RS occurs in thefirst subframe and potentially second subframe of the TxOP, it could bedifficult for the eNB to be able to indicate accurately that the CSI-RSis present on any other carrier than on the same carrier as the UL Grantis sent on, due to processing delay. In that sense, it would be easierto operate CSI-RS configurations if at least two CSI-RS occasions occurwithin a single TxOP occasion, with a maximum difference in time betweenthem. This ensures that the there is always a CSI-RS resource occasionthat is possible for the eNB to indicate to the UE to measure on. Thecurrently defined CSI-RS preiodicities are 5, 10, 20, 40 and 80 ms. Themainly considered TxOP values in the LAA design are currently 4 and 10ms. A CSI-RS with a periodicity of 5 ms can be supported with a TxOP of10 ms. This assumes that the CSI-RS can occur in any subframe within theTxOP. It is worth noting here that DwPTS does not support CSI-RSconfigurations so that, if the last DL subframe is corresponding to aDwPTS subframe, a CSI-RS configuration for such a subframe needs to bedefined. For a TxOP of 4 ms, a new tighter periodicity of CSI-RS needsto be introduced. This is to ensure the presence of two CSI-RS occasionswithin the TxOP. For the case of only having a single CSI-RS occasionwithin a 4 ms TxOP, a 4 ms periodicity is sufficient and for doubleCSI-RS occasion 2 ms periodicity is required. To simplify the eNBprocessing it is proposed to allow that there are at least two CSI-RSoccasions within the applicable TxOP for LAA.

Accordingly, in some embodiments, a CSI-RS periodicity of 2 ms may beintroduced. Given that there are multiple CSI-RS occasions within theTxOP either of the above two discussed solutions for indicating thepresence of the CSI-RS are possible. It is noted that the first approachis based on a specific RNTI that is broadcast and the second approach isbased on the eNB transmitting an UL Grant per UE. The first solutionwould need the use of a common search to indicate the message, which isa limited resource. The second approach however, assumes that the numberof scheduled UEs is rather low. The last assumption is motivated by theLAA SCell being a small cell, which means that is generally not servingas many UEs as a macro cell.

In an embodiment, the presence of CSI-RS is indicated by a UL granttriggering an aperiodic CSI report for the indicated SCell. The othercomponent of the CSI measurement is the interference measurement. Toaccurately represent the interference conditions when data istransmitted to the UE, it would be beneficial for the interference to bemeasured on CSI interference measurement (CSI-IM) when the serving SCellis transmitting. The simplest approach is that the interference ismeasured on CSI-IM resources at the same time when the UE performsmeasurements on the CSI-RS.

In an embodiment, the UE can conduct interference measurements for thepurpose of CSI reporting on CSI-IM resource in the same time occasionsas the UE does measurements on CSI-RS. There is a risk that twodifferent transmitting entities, either eNB, UEs, ST or APs collide overthe air and both grab the channel If the UE would in such an occasionmeasure on a CSI-RS and CSI-IM, the measurement would be very noisy andnot represent the general conditions of the channel Within the currentLTE design, it is allowed for the UE to average CSI-RS and CSI-IMmeasurement across different CSI-RS and CSI-IM occasions. If this occursin the above situation, the measurement error will propagate in time andwould not correspond to the actual CSI at the time of a successfultransmission. It may therefore be preferred to limit CSI-RS and CSI-IMmeasurements to a single CSI-RS and CSI-IM occasion and not allowaveraging over time. Accordingly, an embodiment may include CSI-RS andCSI-IM measurements that are only based on one CSI-RS and CSI-IMoccasion.

In sum, various embodiments may include: LAA SCells that do not supportperiodic CSI reports, but do support aperiodic CSI reports; introduce aCSI-RS periodicity of 2 ms; the presence of CSI-RS is indicated by a ULgrant triggering an aperiodic CSI report for the indicated SCell; thereis no need to change the CSI-IM resource handling; and CSI-RSmeasurements are only based on one CSI-RS occasion.

LBT for LAA UL Transmissions

Different options may be considered for accessing unlicensed spectrumfor LAA uplink transmissions. Moreover, we discuss the necessity toconsider joint designing of the DL and UL LBT algorithms Thisdescription is about the DL and UL LBT dependency.

Frame Based or Load Based LBT for Uplink Transmission

It has been discussed that the load-based CCA procedure is not only verysimilar to the Wi-Fi physical medium sensing procedure, but alsoprovides flexible spectrum utilization and adaptability to traffic load.Therefore, it is recommended that the LBT procedure for LAA be designedbased on the load-based procedure both for UL and DL transmission.Focusing more on the uplink, the frame based LBT may appear to benefitthe UE with power saving and reduced complexity due to the fixed CCAtime. However, the load based LBT is also capable of providing suchbenefits without compromising transmission efficiency due to itsflexibility in accessing the channel as opposed to the frame based LBTprocedure with its rigid structure. The fact that the UE is aware of itsuplink grant 4 ms prior to its corresponding scheduled subframe mayprovide enough time for the UE to choose a reasonable starting point ofCCA.

Also, having the load based LBT approach does not impose unnecessaryconstraints on the eNB to schedule the UEs for the uplink traffic withconsideration to the CCA time as a function of the total transmissionduration depending on the number of subframes the UE is scheduled for asin the case of the frame based approach. The load based LBT providesmore flexibility in the scheduler to better adapt to uplink traffic loadby making the start points of CCA more flexible. Moreover, UE powersaving can be achieved by allowing defer periods in channel sensing whenthe medium is observed to be occupied. For example, a UE that isscheduled for two consecutive subframes starts CCA close to the subframeboundary of the first scheduled subframe. If it fails to succeed in loadbased LBT for that subframe, the UE can defer and continue sensing closeto the next subframe boundary and save power. Note that introducingdefer periods can also ensure better coexistence with Wi-Fi.

Accordingly, an embodiment includes, when an LBT procedure is used foruplink transmission in LAA, using ETSI rules defined for Load BasedEquipment as a starting point.

Mandatory or Optional LBT for Uplink Transmission

Enforcing LBT when it comes to uplink transmissions in LAA has beendiscussed. One embodiment includes a default approach where each UE hasto perform LBT to be permitted for its uplink transmission. Althoughthis approach seems reasonable regarding the basic principles ofaccessing the unlicensed band, it might be possible to relax some of therequirements on UEs to perform LBT prior to uplink transmission withoutresulting in any unfair exploitation of the unlicensed channel withrespect to other transmitting nodes. For example, the number of UEsdoing LBT can be probably reduced in a group of UEs that are locatedclose enough to each other and experience similar observed interference.The possible advantages could be improved UE power saving and possiblymore efficient transmission by avoiding unnecessary LBT attempts.Moreover, there have been further discussions on relaxing all the UEs onperforming LBT for example by sharing the corresponding eNB channelaccess for uplink transmissions.

Moreover, the discussion of DL+UL LAA is starting and there isconsiderable range of uncertainty at this point. Note that ULtransmission in LTE is not autonomous from the UE side but is controlledand scheduled by the eNB. Hence, in the case of self-scheduling, ULtransmissions can happen only if the LAA eNB gain channel access first.Consider the scenario where the LAA network (with 1 LAA eNB +N LAA UEs)is operating on the channel with a Wi-Fi network (with 1 Wi-Fi AP +NWi-Fi stations). Two first-order considerations are made. First, if theLAA eNB can only gain channel access share on the order of 1/N, thescheduled UEs following similar LBT algorithms will gain channel accesson the order of 1/N. The net channel access share of the LAA UEs is then1/N². This type of solution may not achieve a fair sharing of the DL+ULoperations for the LAA network. Second, if the LAA eNB can gain channelaccess share on the order close to ½, the scheduled UE can adopt an LBTalgorithm such that they will gain channel access on the order of 1/N.The net channel access share of the LAA UEs is then ½N.

With the above considerations, it is recognized that the LBT attempts atUE for LAA uplink transmissions could be considered mandatory for allUEs, optional for some of the UEs or not required for any of the UEs.Each of the three alternatives differently impact UE power saving andtransmission efficiency. In the LTE protocol, UL transmissions arecontrolled by the eNB through UL grants given to individual UEs.

Accordingly, in some cases, there may be three alternatives for uplinkLBT: 1) LBT mandatory for all UEs; 2) LBT optional for some UEs; and 3)LBT not required for all UEs. Uplink LBT should consider the dependencyof LTE UL transmissions to DL transmissions through UL grants. In somecases, UL LBT should ensure that the eNB and its serving UEs wouldbenefit a fair sharing of the spectrum in spite of the dependency of LTEUL transmissions to DL transmissions through UL grants.

In sum, potential alternatives for performing LBT at UE side for the LAAuplink transmission are considered. In some embodiments, when an LBTprocedure is used for uplink transmission in LAA, ETSI rules defined forLoad Based Equipment are considered as a starting point. In some cases,the LBT attempts at UE for LAA uplink transmissions could be consideredmandatory for all UEs, optional for some of the UEs or not required forany of the UEs. Each of the three alternatives differently impacts UEpower saving and transmission efficiency. In the LTE protocol, ULtransmissions may be controlled by the eNB through UL grants given toindividual UEs. Three alternatives for uplink LBT may include LBTmandatory for all UEs, LBT optional for some UEs and LBT not requiredfor any of the UEs. Uplink LBT should consider the dependency of LTE ULtransmissions to DL transmissions through UL grants. UL LBT may ensurethat the eNB and its serving UEs would benefit a fair sharing of thespectrum in spite of the dependency of LTE UL transmissions to DLtransmissions through UL grants.

LBT for LAA DL Transmissions

Detailed solutions for the LBT phase in LAA have been discussed in orderto ensure fair coexistence with Wi-Fi and other LAA services as well ascompliance with regulatory requirements. Here, further details fordesign of LBT in the downlink for LAA are considered.

Regarding LBT design in DL for LAA, the benefits of a load-based LBTscheme were discussed due to its flexible spectrum utilization andadaptability to traffic load and proposed an LBT protocol, which ensuresfair coexistence with other technologies in particular Wi-Fi in theunlicensed spectrum. In some LBT protocol embodiments with additionalcoexistence measures, additional deferring after sensing an occupiedchannel and before post-transmission random backoff are added to the EN301.893 generic load-based LBT procedure to enable better coexistencebehavior with Wi-Fi and LAA. The modification provides a means torandomize LAA data transmissions.

In some embodiments, the following LAA LBT procedure is used. Asillustrated with a flow chart in FIG. 26, a random backoff counter, N,is always drawn to start the LBT procedure. An initial CCA isimmediately followed by an extended CCA stage. For example, an initialCCA is performed for duration To and continued if busy. If the carrieris found to be idle and if N is not greater than 0, transmission isperformed. If N is greater than 0, CCA is performed for duration T₁. Ifbusy, CCA is performed again with duration To. If idle, the N counter isdecremented and it is determined whether N is greater than 0. If not,transmission occurs. If N is still greater than 0, CCA is performedagain for duration T₁.

In other words, a successful transmission leads to a restart of the LBTprocedure with a newly drawn random backoff counter, N. This ensuresthat a defer period and a post-transmission random backoff with extendedCCA is employed after the end of every transmission burst. Defer periodsare incorporated by freezing the backoff counter and deferring back tothe initial CCA when the channel is observed to be occupied during theextended CCA.

Some features may be adjusted to enhance the flexibility and efficiencyof the LBT protocol with consideration to at least the followingobjectives: reducing UE complexity and power consumption; reducingoverhead; imposing minimum standardization impact; and reducingcollision and avoiding channel access starvation.

Regarding freeze periods during a load-based LBT procedure, the startingtime instance of the LBT procedure at eNB can be flexible and when eNBis permitted to access the channel it can transmit signals. However, theeNB can be configured to consider time periods during the LBT procedurewhere no transmission can be initiated within. These time periods can bereferred to as “the freeze periods” for simplicity. The initiation oftransmission due to the successful LBT can be hence occurred onlyoutside these time intervals.

Configuring freeze periods at eNB during the LBT procedure enhances thecorresponding UEs power saving due to the fact that those UEs are notexpecting any possible transmission during the freeze periods, since theeNB remains idle during the freeze periods. Moreover, it reduces theoverhead due to the possible transmission of the initial/reservationsignals. Additionally, this feature increases the opportunities forother contending nodes in the medium to access the channel in aneffective manner which can serve a purpose similar to the exponentialbackoff feature in Wi-Fi technology.

Moreover, the eNB can be configured to have a limited time budget forthe CCA operation in the LBT procedure. As an example, the EN ETSI301.893 generic load-based LBT regulation implies that a contentionwindow of 10 is large enough to fulfil a maximum channel occupancy of 4ms. This means that for the LBT with a CCA slot of 20 μs, if the largestrandom backoff number is drawn, a time budget of about 3 OFDM symbols(OS) is required for the LBT to declare success if the channel is idle.

FIGS. 27 and 28 show some illustrative examples of how configuration offreeze periods and limited CCA budget would impact the LBT procedure,according to some embodiments. The examples provided in these figuresshow that there is a trade-off between the level of politeness and theoverhead with configuration of the freeze periods. The larger the freezeperiods, the more polite the LBT protocol is towards other systems andthe smaller the overhead due to the potential initial/reservationsignals. However, it is important to keep in mind that freeze periodsshould not result in starving an eNB by being completely disadvantagedin accessing the channel as compare to the other nodes. In other words,this feature is applicable when the system is operating in a stablepoint, otherwise reducing or discarding the freeze period is preferable.FIG. 27 illustrates an LBT protocol with or without freeze periods in amedium load scenario. FIG. 28 illustrates some examples ofself-scheduling on SCell for LAA eNBs with the constraint of 4 msmaximum channel occupancy time.

Fixed OS candidates may be used to initiate data transmission after asuccessful LBT procedure. Moreover, fixed candidates for initiating thedata transmission can reduce the complexity at the UE side where thedata would be expected to start arriving in limited time instances.

In the following, corresponding approaches are considered to supportEPDCCH and PDCCH self-scheduling. The UE can be configured with eitherself-scheduling or cross-carrier scheduling. For efficient operations onLAA, self-scheduling has higher importance for being supported since itreduces the scheduling load on the PCell. Moreover, cross-carrierscheduling can have challenges due to the very short delay between theLBT result on the SCell and the scheduling command on the PCell, andcross-carrier scheduling can impose scheduling limitations if thescheduling cell is operating TDD.

In some embodiments, to support self-scheduling with EPDCCH on the LAASCell, EPDCCH resources should be configured for the SCell. To reducethe UEs complexity, the UE may be configured with one fixed candidatefor the EPDCCH starting OS which already exists in the standard. Theproper choice of the EPDCCH starting OS depends on the operating pointof the LBT protocol. The example in FIG. 29 shows that the EPDCCH alwaysstart in OS #3 irrespective of where the subframe is located in atransmission burst based on the CCA time budget of 3 OFDM symbols thatwas discussed earlier. As shown in this figure, there are only two OScandidates for PDSCH starting symbols, being OS#0 and OS#3. A new fieldmay be needed in the DCI to indicate to the UE whether the subframe is anormal subframe (with PDSCH occupying all 14 OS) or a shortened subframe(with DPSCH occupying 11 OS starting at OS #3). From the UE's point ofview, the UE checks its allocated EPDCCH search space(s) when it is notin DRX. When CRC checks for a searched EPDCCH candidate, the UE canfollow the DCI to correctly decode the PDSCH transmission.

In some cases, to support self-scheduling with PDCCH on the LAA SCell,only OS#0 can be considered for starting the data transmission to reducethe impact on the PDDCH. However, this implies that in order to releasethe channel as late as possible, the last subframe has to be shortenedat the end that would impact demodulation reference signals (DMRS) andsome CSI-RS configurations. Moreover, that subframe from the UE sideshould be configured differently than other subframes and use a similarstructure as downlink pilot time slot (DwPTS), where the last OFDMsymbol with CRS may not be available. FIG. 28 illustrates some examplesof self-scheduling on SCell for LAA eNBs with the constraint of 4 msmaximum channel occupancy time. For example, the LBT protocol may bewith or without freeze periods in a heavily occupied medium.

However, support of DMRS-based transmission modes may be preferred ascompared to the CRS-based transmission modes. This is motivated by thefact that in the context of discontinuous transmission on the LAA SCell,the legacy CRS does not exist as in previous releases. In fact, the CRScan be present only in the subframes that transmission is allowed. Duethe unpredictable nature of the unlicensed band there is no guaranteefor the existence of CRS even if enhanced International MobileTelecommunications Advanced (eIMTA) frame work is adopted for LAA.Therefore, the standardization impact in particular on the testsprocedures and requirements in RAN4 in relation to non-always availableCRS may be significant. This statement holds even if DRS frame work orTDD configuration 0 are considered as a starting point since all rely onthe periodicity of the CRS but less frequent. The situation for DMRSbased transmission is different since DMRS is present only when data ispresent. Hence no changes in the specifications are needed as comparedto CRS but perhaps some new requirements are needed to specify.

Having said that, the freeze period feature is in general applicable tosupport both DMRS based or CRS based transmissions, as shown in FIG. 30.Accordingly, in some embodiments, freeze periods during the LBTprocedure may be configured at the eNB where the UE does not expect anysignal form eNB is supported. Self-scheduling may be based on EPDCCHshould be considered for LAA SCells. For DMRS-based transmission the UEmay be configured with one of the four candidates of the EPDCCHstarting. A candidate with an offset from the subframe boundary may bepreferred. A maximum channel occupancy of 4 ms may suggest OS#3 as thestarting symbol for EPDCCH. FIG. 29 illustrates examples on LAAself-scheduling on the SCell with maximum channel occupancy of 4 ms. Anew control bit in the DCI message may indicate to the UE starting pointof the PDSCH. The default may be a choice between two alternatives ofOS#0 and OS#3.

Prioritized Channel Access

In some embodiments, a Wi-Fi enhanced distributed channel access (EDCA)mechanism defines four access categories (ACs) to support prioritizedquality of service (QoS). Each AC is characterized by specific valuesfor a set of access parameters that statistically prioritize channelaccess for one AC over another.

In LAA, a similar prioritization of channel access could be defined. Oneoption is to apply different LBT categories to prioritize channel accessfor different channels and signals, or support data with different QoSrequirements in LAA. For example, it would be beneficial to have aprioritized channel access for management and control information overdata traffic in LAA. Examples of management and control information canbe Discovery Reference Signal (DRS) transmissions, or Master InformationBlock (MIB) and/or System Information Block (SIB) signals, etc. Adifferent LBT scheme than the LBT procedure proposed in FIG. 26 can beapplied for channel access of management and control information, asshown in FIG. 31.

The transmissions can commence immediately after the initial CCA iscleared. If the channel is determined to be busy during an initial CCA,the commencement of the next CCA is conditionally deferred to the nextCCA starting point. Therefore, the management and control informationcould have a prioritized channel access and have higher probability tobe transmitted at the predetermined time instances, which could beespecially beneficial for DRS transmission and in turn would facilitateand simplify the DRS reception on UE side.

Another option is to apply different LBT parameters to prioritizechannel access for different channels and signals, or support data withdifferent QoS requirements in LAA. The channel access may beprioritized/deprioritized using different LBT parameter settings, suchas the CCA duration, freeze periods, contention window sizes, etc. Forthe channels or signals with a prioritized channel access, for example,with a smaller contention window size, the maximum channel occupancytime can be decreased to maintain a fair coexistence. Accordingly, inembodiment may include supporting prioritized channel access in LAA by,for example, applying different LBT categories, and/or different LBTparameters, etc. For prioritized channel access, the channel/signal withprioritized access should be determined and specified. One example isthat DRS should have a prioritized channel access over othertransmissions in DL. Moreover, the LBT scheme and LBT parameters need tobe specified for the prioritized channel/signal.

In sum, further details on DL LBT in LAA were explained and someembodiments may include the following in the LBT procedure for LAA datatransmissions: a random backoff counter, N, is always drawn to start theLBT procedure; an initial CCA is always immediately followed by anextended CCA stage; a successful transmission always leads to a restartof the LBT procedure with a newly drawn random backoff counter, N. Thismay ensure that a defer period and a post-transmission random backoffwith extended CCA is employed after the end of every transmission burst.Defer periods may be incorporated by freezing the backoff counter anddeferring back to the initial CCA when the channel is observed to beoccupied during the extended CCA. Freeze periods during the LBTprocedure may be configured at the eNB where the UE does not expect anysignal from the eNB. Self-scheduling may be based on EPDCCH should beconsidered for LAA SCells. For DMRS-based transmission, the UE may beconfigured with one of the four candidates of the EPDCCH starting. Acandidate may include an offset from the subframe boundary. Maximumchannel occupancy of 4 ms may suggests OS#3 as starting symbol forEPDCCH. A new control bit in the DCI message may indicate to the UEstarting point of the PDSCH. The default may be a choice between twoalternatives of OS#0 and OS#3. Prioritized channel access may besupported in LAA, for example, by applying different LBT categories,and/or different LBT parameters, etc.

Notably, modifications and other embodiments of the disclosedinvention(s) will come to mind to one skilled in the art having thebenefit of the teachings presented in the foregoing descriptions and theassociated drawings. Therefore, it is to be understood that theinvention(s) is/are not to be limited to the specific embodimentsdisclosed and that modifications and other embodiments are intended tobe included within the scope of this disclosure. Although specific termsmay be employed herein, they are used in a generic and descriptive senseonly and not for purposes of limitation.

1-44. (canceled)
 45. A method performed at a wireless device, thewireless device being connected to a cell operated by a network node,wherein the cell is configured on a carrier where a listen-before-talk(LBT) protocol for transmission is required to be used, the methodcomprising: receiving a scheduling grant from the network node;receiving, from the network node, a grant confirmation signal indicatingthat the network node has performed a clear channel assessment (CCA) onthe carrier and is releasing the carrier for the wireless device; andresponsive to receiving the scheduling grant and the grant confirmationsignal, transmitting an uplink message on the carrier without performinga CCA on the carrier.
 46. The method of claim 45, wherein the grantconfirmation signal is received in, or subsequent to, the subframebefore the first scheduled subframe according to the scheduling grant.47. The method of claim 45, further comprising determining a location ofthe grant confirmation signal according to a specification.
 48. Themethod of claim 45, further comprising determining a location of thegrant confirmation signal according to a configuration signaled via ahigher layer.
 49. A method performed at a network node, the network nodeserving a cell, wherein the cell is configured on a carrier where alisten-before-talk (LBT) protocol for transmission is required to beused and wherein at least one wireless device is connected to the cell,the method comprising: transmitting a scheduling grant to a wirelessdevice for the carrier, for a scheduled uplink transmission; performinga first clear channel assessment (CCA) for the carrier, prior to a timefor the scheduled uplink transmission; and responsive to success of thefirst CCA, transmitting a grant confirmation signal to the wirelessdevice and releasing the carrier for the scheduled uplink transmission.50. The method of claim 49, wherein the grant confirmation signalcomprises an indication of the number of subframes for which channelaccess has been secured.
 51. The method of claim 49, whereintransmitting the scheduling grant is preceded by performing a second CCAfor the carrier.
 52. The method of claim 49, further comprisingtransmitting scheduling grants to each of more than one wireless deviceresponsive to the first CCA being successful.
 53. The method of claim52, further comprising scheduling all of the more than one wirelessdevices in each of every subframe for which channel access has beensecured by performing the first CCA and releasing the carrier.
 54. Themethod of claim 52, further comprising scheduling at least one wirelessdevice for fewer than all of the subframes in a series of subframes forwhich channel access has been secured by performing the first CCA andreleasing the carrier, and wherein the grant confirmation signaltransmitted to the at least one wireless device indicates the number ofsubframes for which channel access has been secured.
 55. The method ofclaim 49, wherein the first CCA is performed a predetermined number ofsubframes after transmitting the scheduling grant.
 56. The method ofclaim 55, wherein the predetermined number of subframes is three. 57.The method of any of claim 49, further comprising receiving an uplinktransmission from the wireless device after transmitting the grantconfirmation signal.
 58. The method of claim 57, where the uplinktransmission is received in the subframe immediately following asubframe in which the grant confirmation signal was transmitted.
 59. Amethod performed at a wireless device, the wireless device beingconnected to a first cell and a second cell, wherein the second cell isconfigured on a carrier where a listen-before-talk (LBT) protocol fortransmission is required to be used, the method comprising: receivingone or more configuration messages indicating that downlinktransmissions on the second cell are to be scheduled; receiving ascheduling grant in the first cell; in a subframe occurring apredetermined number of subframes after receiving the scheduling grant,performing a clear channel assessment (CCA) in the second cell; andtransmitting an uplink message responsive to success of the CCA.
 60. Themethod of claim 59, wherein the one or more configuration messagesindicate that downlink transmissions on the second cell are to bescheduled using self-scheduling on the second cell, and that uplinktransmissions on the second cell are to be scheduled using cross-carrierscheduling on the first cell.
 61. A method performed at a network node,the network node serving a first cell and a second cell, wherein thesecond cell is configured on a carrier where a listen-before-talk (LBT)protocol for transmission is required to be used, the method comprising:transmitting, to a wireless device, one or more configuration messagesindicating that downlink transmissions on the second cell are to bescheduled; transmitting a scheduling grant to the wireless device in thefirst cell; and receiving an uplink message from the wireless device inthe second cell, according to the transmitted scheduling grant.
 62. Themethod of claim 61, wherein the one or more configuration messagesindicate that downlink transmissions on the second cell are to bescheduled using self-scheduling on the second cell, and that uplinktransmissions on the second cell are to be scheduled using cross-carrierscheduling on the first cell.
 63. A wireless device connected to a celloperated by a network node and configured to be connectable to a cellconfigured on a carrier where a listen-before-talk (LBT) protocol fortransmission is required to be used, wherein the wireless device isconfigured to: receive a scheduling grant from the network node;receive, from the network node, a grant confirmation signal indicatingthat the network node has performed a clear channel assessment (CCA) onthe carrier and is releasing the carrier for the wireless device; andresponsive to receiving the scheduling grant and the grant confirmationsignal, transmit an uplink message on the carrier without performing aCCA on the carrier.
 64. The wireless device of claim 63, wherein thewireless device is configured to receive the grant confirmation signalin, or subsequent to, the subframe before the first scheduled subframeaccording to the scheduling grant.
 65. The wireless device of claim 63,wherein the wireless device is configured to determine a location of thegrant confirmation signal according to a specification.
 66. The wirelessdevice of claim 63, wherein the wireless device is configured todetermine a location of the grant confirmation signal according to aconfiguration signaled via a higher layer.
 67. A network node configuredto serve a cell on a carrier where a listen-before-talk (LBT) protocolfor transmission is required to be used, the network node being furtherconfigured to: transmit a scheduling grant to a wireless device for thecarrier, for a scheduled uplink transmission; perform a first clearchannel assessment (CCA) for the carrier, prior to a time for thescheduled uplink transmission; and responsive to success of the firstCCA, transmit a grant confirmation signal to the wireless device andrelease the carrier for the scheduled uplink transmission.
 68. Thenetwork node of claim 67, where the network node is one of: a Long TermEvolution (LTE) eNodeB; and a Wi-Fi access point.
 69. The network nodeof claim 67, wherein the grant confirmation signal comprises anindication of the number of subframes for which channel access has beensecured.
 70. The network node of claim 67, wherein the network node isconfigured to perform a second CCA for the carrier, preceding thetransmission of the scheduling grant to the wireless device.
 71. Thenetwork node of claim 67, wherein the network node is configured totransmit scheduling grants to each of more than one wireless device,responsive to the first CCA being successful.
 72. The network node ofclaim 71, wherein the network node is configured to schedule all of themore than one wireless devices in each of every subframe for whichchannel access has been secured by performing the first CCA andreleasing the carrier.
 73. The network node of claim 71, wherein thenetwork node is configured to schedule at least one wireless device forfewer than all of the subframes in a series of subframes for whichchannel access has been secured by performing the first CCA andreleasing the carrier, and wherein the grant confirmation signaltransmitted to the at least one wireless device indicates the number ofsubframes for which channel access has been secured.
 74. The networknode of claim 67, wherein the network node is configured to perform thefirst CCA a predetermined number of subframes after transmitting thescheduling grant.
 75. The network node of claim 74, wherein thepredetermined number of subframes is three.
 76. The network node ofclaim 67, wherein the network node is configured to receive an uplinktransmission from the wireless device after transmitting the grantconfirmation signal.
 77. The network node of claim 76, where the networknode is configured to receive the uplink transmission in the subframeimmediately following a subframe in which the grant confirmation signalwas transmitted.
 78. A wireless device configured to be connectable to afirst cell and a second cell, wherein the second cell is configured on acarrier where a listen-before-talk (LBT) protocol for transmission isrequired to be used, wherein the wireless device is configured to:receive one or more configuration messages indicating that downlinktransmissions on the second cell are to be scheduled; receive ascheduling grant in the first cell; in a subframe occurring apredetermined number of subframes after receiving the scheduling grant,perform a clear channel assessment (CCA) in the second cell; andtransmit an uplink message responsive to success of the CCA.
 79. Thewireless device of claim 78, wherein the one or more configurationmessages indicate that downlink transmissions on the second cell are tobe scheduled using self-scheduling on the second cell, and that uplinktransmissions on the second cell are to be scheduled using cross-carrierscheduling on the first cell.
 80. A network node configured to serve afirst cell and a second cell, wherein the second cell is configured on acarrier where a listen-before-talk (LBT) protocol for transmission isrequired to be used, wherein the network node is configured to:transmit, to a wireless device, one or more configuration messagesindicating that downlink transmissions on the second cell are to bescheduled; transmit a scheduling grant to the wireless device in thefirst cell; and receive an uplink message from the wireless device inthe second cell, according to the transmitted scheduling grant.
 81. Thenetwork node of claim 80, wherein the one or more configuration messagesindicate that downlink transmissions on the second cell are to bescheduled using self-scheduling on the second cell, and that uplinktransmissions on the second cell are to be scheduled using cross-carrierscheduling on the first cell.
 82. A non-transitory computer-readablemedium comprising, stored thereupon, a computer program productcomprising program instructions that, when executed by a processor in awireless device connected to a cell operated by a network node, whereinthe cell is configured on a carrier where a listen-before-talk (LBT)protocol for transmission is required to be used, causes the wirelessdevice to operate so as to: receive a scheduling grant from the networknode; receive from the network node, a grant confirmation signalindicating that the network node has performed a clear channelassessment (CCA) on the carrier and is releasing the carrier for thewireless device; and responsive to receiving the scheduling grant andthe grant confirmation signal, transmit an uplink message on the carrierwithout performing a CCA on the carrier.
 83. A non-transitorycomputer-readable medium comprising, stored thereupon, a computerprogram product comprising program instructions that, when executed by aprocessor in a network node serving a cell, wherein the cell isconfigured on a carrier where a listen-before-talk (LBT) protocol fortransmission is required to be used, causes the network node to operateso as to: transmit a scheduling grant to a wireless device for thecarrier, for a scheduled uplink transmission; perform a first clearchannel assessment (CCA) for the carrier, prior to a time for thescheduled uplink transmission; and responsive to success of the firstCCA, transmit a grant confirmation signal to the wireless device andreleasing the carrier for the scheduled uplink transmission